1. Field of the Invention
The present invention relates to an optical disk drive apparatus for reproducing data in a constant linear velocity made and a method of arithmetically determining or calculating the linear velocity of the disk.
2. Description of Related Art
As is well known in the art, optical disk recording midia are capable of recording or storing a large amount of data with a high recording density. In recent years, many-sided activities have been made in efforts to develop the optical disk of enhanced performance and find practical applications thereof. As a typical one of the applications of the optical disk, there may be mentioned a compact-disk read-only memory device known as the CD-ROM drive and developed on the basis of the optical disk which is intrinsically designed for reproduction of pieces of music and known also as the CD for short.
With the compact-disk read-only memory (hereinafter also referred to simply as the CD-ROM), a large-capacity recording medium having a recording or storage capacity of about 650 mega-bytes (MB) can be realized by using an optical disk of 12 cm in diameter and resorting to a constant-linear-velocity reproduction mode. Furthermore, a write-once optical disk known a recordable compact disk or CD-R has also been developed in addition to optical disks designed only for the reproduction.
To provide better understanding of the technical background of the invention, description will first be made of a conventional optical disk drive apparatus designed for reproducing data at a constant linear velocity by taking as an example a CD-ROM drive designed for reproducing data at a constant linear velocity. FIG. 10 of the accompanying drawings is a block diagram showing schematically a structure of a conventional optical disk drive known heretofore. In the figure, reference numeral 1 denotes an optical disk having data recorded at a constant linear velocity, numeral 2 denotes an optical pickup for reading out the data recorded on the optical disk 1, numeral 3 denotes a servo controller for controlling the optical pickup 2 so that it follows data trains recorded on the optical disk 1, numeral 4 denotes a reproduced signal detector for detecting and converting the reproduced signal a outputted from the optical pickup 2 into a binary signal, numeral 7 denotes a spindle motor for rotationally driving the optical disk 1 mounted on the spindle motor 7, and numeral 8 denotes a spindle driver circuit for driving the spindle motor 7 under the control of a disk rotation controller 15 which will be described in detail later on. Further, reference numeral 9 denotes a synchronous clock generator which is comprised of a phase comparator 11a, a loop filter 12 and a voltage-controlled oscillator (VCO) 10, as will be described hereinafter. The disk rotation controller 15 is composed of a phase comparator 11b, a frame detector 19, a second reference oscillator 20, a first reference oscillator 21 and a maximum time duration detector 22, as will be described in detail hereinafter. Furthermore, reference numeral 16 denotes a signal processor which serves for writing or storing the data train (or series of data) read out from the optical disk in a memory, demodulating the data train and preforming an error correction/concealment processing for the data before sending it to an external circuit or apparatus.
The voltage-controlled oscillator 10 is designed to change the oscillation frequency of the clock signal outputted therefrom in dependence on an input voltage applied to the oscillator 10. In this conjunction, the voltage-controlled oscillator 10 is imparted with a wide frequency-variable range so that the data can be read out from the optical disk even when the optical disk is driven at a rotation speed outside of a specified rotation speed. The phase comparator 11a functions to compare the phase of the binary reproduced signal b with that of the clock signal outputted from the voltage-controlled oscillator 10 to thereby generate a phase difference signal. On the other hand, the loop filter 12 serves for eliminating high-frequency noise components from the phase difference signal outputted from the phase comparator 11a. Thus, the response characteristics of the synchronous clock generator 9 are essentially determined by the loop filter 12.
Referring again to FIG. 10, the phase comparator 11b serves for detecting a phase difference between the output signal of the frame detector 19 and that of a second reference oscillator 20. The frame detector 19 in turn serves for detecting a frame-synchro-nous signal on the basis of the synchronous clock signal derived from the binary reproduced signal. The second reference oscillator 20 operates to output a second reference clock signal, while the first reference oscillator 21 is designed to output a first clock signal. The maximum time duration detector 22 is so implemented as to detect a maximum time duration of bit pattern from the binary reproduced signal b.
Now, description will turn to operation of the conventional optical disk drive apparatus of the structure described above. The data trains recorded on the optical disk 1 are read out by the optical pickup 2. In that case, the servo controller 3 controls the optical pickup 2 such that the optical pickup 2 follows the data trains to be picked up independent of fluctuations and/or eccentricity of the plane of the optical disk 1. The reproduced signal detector 4 serves for digitizing the reproduced signal a read out from the optical disk 1 by the optical pickup 2 (i.e., conversion of the output signal of the optical pickup 2 into a binary signal). For convenience's sake of description, the binary signal outputted from the reproduced signal detector 4 is referred to also as the binary reproduced signal.
The maximum time duration detector 22 detects the maximum time duration (corresponding to an elevenchannel clock length in the case of the CD-ROM) of the bit pattern from the binary reproduced signal b to compare the detected duration with a number of counts (hereinafter also referred to as the count number) by counting the output clock pulses of the first reference oscillator 21. At this juncture, it should be mentioned that the maximum time duration mentioned above corresponds to the linear velocity of the optical disk in the reproducing operation mode. In dependence on the result of the comparison mentioned above, the maximum time duration detector 22 outputs a rotation control signal c such that the rotation speed of the spindle motor 7 is increased when the maximum time duration is short in the relative sense while lowering the rotation speed of the spindle motor 7 when the maximum time duration is long. The spindle driver circuit 8 drives the spindle motor 7 in conformance with the rotation control signal c outputted from the maximum time duration detector 22. In that case, the rotation speed of the spindle motor 7 is accelerated, being controlled roughly, without resorting to the servo-control. This acceleration phase is continued up to a time point at which the output of the synchronous clock generator 9 reaches a range in which the binary reproduced signal b can be pulled into synchronization.
The synchronous clock generator 9 is generally known as the phase-locked loop circuit (PLL circuit) and implemented in such structure as mentioned below. Namely, as shown in a broken-like block in FIG. 10, the synchronous clock generator 9 is constituted by the phase comparator 11a for comparing the phase of the binary signal with the output of the voltage-controlled oscillator 10 to thereby output the phase difference signal, the loop filter 12 for eliminating the high-frequency noise components from the phase difference signal, which thus determines the response characteristics of the phase-locked loop circuit 9, and the voltage-controlled oscillator 10 whose output clock oscillation frequency changes in dependence on the output voltage of the loop filter 12. The phase-locked loop circuit (i.e., the synchronous clock generator 9) generates the synchronous clock signal for the reproduction of data. In succession to the rough rotation control, the synchronous clock generator 9 pulls the binary reproduced signal b into synchronization, whereby the synchronous clock signal is generated.
Recorded on the optical disk 1 are the data trains, which are also referred to as the frames, on a block-by-block basis, wherein a pair of patterns having the maximum time duration and referred to as the frame-synchronous signal are recorded at a leading portion of the frame. The rotation control of the optical disk 1 (or the control of the spindle motor 7) after establishment of synchronization with the synchronous clock generator 9 is so performed that the interval of the frame-synchronous signal for detection of the rotation speed remains constant by making use of the frame-synchronous signal for detecting the rotation speed. Owing to the control described above, the optical disk 1 can be so controlled that the linear velocity thereof is maintained to be constant with high accuracy.
Next, description will be directed to the detail of the rotation control based on the frame-synchronous signal. The frame detector 19 detects the frame-synchronous signal on the basis of the synchronous clock derived from the binary reproduced signal b. Since the frame-synchronous signal is generated at a periodic rate corresponding to the linear velocity in the reproduction mode, it is possible to control the spindle motor 7 so that the frame-synchronous signal remains constant by detecting the phase difference between the frame-synchronous signal and the output clock of the second reference oscillator 20. In this manner, the data on the optical disk 1 are read out while controlling the linear velocity of the optical disk 1.
By the way, in order to read out a given train of data from the optical disk 1, it is required to move the optical pickup 2 at a high speed to the destination address, i.e., a location where the given data is recorded. Operation of moving the optical pickup to the destination address is referred to as the seeking or seek operation. In order to realize the seek operation at a high speed, it is preferred to perform the seek operation at a high speed in the radial direction of the optical disk 1 by traversing the record tracks instead of moving the optical pickup 2 along the circular track on the optical disk 1 for seeking the destination address. Parenthetically, the operation for causing the optical pickup 2 to move to the destination address in the circumferential direction for reading out the data or addresses sequentially will hereinafter be referred to as the sequential read operation. When the radial seek operation of the optical pickup 2 is performed, the optical pickup 2 is caused to move to a track located in the vicinity of the destination address while counting the number of tracks traversed by the optical pickup 2 because the optical disk 1 is incapable of reading the data from the optical disk 1 in the course of radially traversing the tracks. For the convenience's sake of description, the track traversing operation for moving the optical pickup 2 to the location in the vicinity of the destination address will hereinafter be referred to as the track jump operation or simply as the track jump. In succession to the track jump, the address at which the optical pickup 2 has reached is checked or confirmed, whereupon the track jump operation is repeated in dependence on the number of tracks remaining to be traversed by the pickup for reaching the destination address or alternatively the optical pickup 2 is moved to the location of the destination address by performing the sequential read operation. Through the procedure mentioned above, it is possible to make access to the given or desired data for reading out the same.
For realizing the track jump, it is required to make available in precedence the information concerning the number of tracks over which the optical pickup 2 has to jump. In order to obtain such track number information, it is necessary to know the current address of the optical pickup 2, the destination address and the linear velocity of the optical disk 1. In this junction, the current address and the destination address can be derived from the specifications data of the CD-ROM drive. Accordingly, what is important is to know or determine the linear velocity.
According to the standards imposed on the CD-ROM drive, it is recommended that the linear velocity of the optical disk 1 should fall within a range of 1.2 to 1.4 m/sec. Because of such permissible range for the linear velocity, it is naturally expected that the linear velocity adopted in the data recording operation becomes different from one to another optical disk. Such being the circumstances, when the linear velocity differing from that used for the recording of data is employed for reading out or reproducing the data from the optical disk 1, error will be involved in the arithmetic determination or calculation of the number of tracks to be jumped over in order that the optical pickup 2 reaches the destination address, as a result of which the optical pickup 2 is forced to try the track jump operation a number of times, which in turn makes it difficult or impossible for the optical pickup 2 to reach the destination address. For this reason, there arises the necessity of knowing beforehand the linear velocity of the optical disk 1 as precisely as possible.
Heretofore, several methods of knowing the linear velocity which differs from one to another optical disk have been proposed. According to one of such conventional methods, the CD-ROM drive is preset to a given linear velocity upon starting the operation of the CD-ROM drive, whereon difference between the number of tracks to be jumped over and the number of tracks actually jumped over is determined to thereby correct the preset linear velocity, while according to another method, a constant linear velocity is employed for a given optical disk.
However, the first mentioned method, i.e., the method of correcting the preset linear velocity with the difference between the number of tracks to be jumped over by the optical pickup 2 and the number of tracks actually jumped over suffers from shortcomings that a lot of time is taken for the linear velocity converges to a definite value or the linear velocity may undergo erroneous correction when the preset number of tracks is failed to be jumped over. In other words, the conventional linear velocity correcting method suffers a drawback that the linear velocity becomes different every time the linear velocity is corrected.
On the other hand, the method of adopting the constant linear velocity independent of the optical disks is disadvantageous in that for a given optical disk, a linear velocity differing from the real linear velocity of the given optical disk may be set. More specifically, when the linear velocity differing from the real linear velocity is set, the performance of the seek time is degraded in proportion to the magnitude of the difference or error, with the seek time increasing considerably, giving rise to a problem.
Such being the circumstances, there exists a great demand for an optical disk drive apparatus and a linear velocity calculating method capable of calculating the linear velocity with high accuracy so as to realize the track jump operation precisely.